In security monitoring systems, accuracy of motion and intrusion sensors are very important. Currently, motion sensors commonly used for security monitoring systems include passive infrared (PIR) motion sensors and radio frequency doppler (RFD) motion sensors. Power consumption of the passive infrared motion sensors is very low and it is suitable for battery powered security monitoring system applications. The disadvantages of using PIR motion sensors include high false alarm rate. For example, as shown in FIG. 1, vehicles 191, 193, 195, and 197 parked outside of a window 153 may emit certain amount of infrared radiation through the window 153. A PIR motion sensor 100 installed on one side of an area 11 may detect the infrared radiation from vehicles 193 and 195 through the window 153. If the vehicles 193 and 195 drive into or out of the parking spots, the sensor 100 may detect the vehicle motion and trigger an alarm system the sensor 100 is connected to so that a false alarm is raised. On the other hand, RFD motion sensors detect object motion by detecting doppler effects of radio wave reflection of the moving object. For example, as shown in FIG. 1, movements of a few trees, including 171, 173, 175, 177, and 179 outside of the area 11 may be detected by a RFD motion sensor 100 because the radio frequency radiation of the RFD motion sensor is able to penetrate a wall 151. The RFD motion sensors is not sensitive to infrared radiation, but power consumption of the RFD motion sensors is relatively high and it is not suitable for battery powered security monitoring system application continuously operating for a long time. Additionally, when more than one RFD motion sensors having similar radio frequency ranges are used in an area at the same time, different RFD motion sensors may interfere with each other and cause false alarms.
Therefore, a heretofore unaddressed needs still exist in the art to address the aforementioned deficiencies and inadequacies.